1. Field of the Invention
The invention relates to a method for recovering residual matter which accumulates in the production and in the machining of steel. The material recovered is in the form of metal-containing dust and chips and, after the addition of a binder, is formed into briquettes.
2. The Prior Art
The value of recovering residual matter generated when steel is produced and when it is machined has been recognized for a long time but its importance has increased greatly in recent times due to developing shortages of raw materials and the difficulties of finding suitable disposal sites for material that is not recovered. The residual matter has a high metal content consisting of iron and expensive alloying elements, such as chromium and nickel, and recovering the components reduces the need for more expensive raw materials. To this must be added that the transportation and disposal of the residual matter, which is usually present in the form of fine dust, raises problems with respect to pollution of the environment.
Thus, numerous proposals have been made for reprocessing residual matter with the goal of re-using it in the production of steel.
From DE-AS No. 23 61 742, for instance, a method is known, according to which spherical briquettes are made from four components, namely, sludge, a coarse component with a grain size&gt;100 .mu.m, a fine component with a grain size&lt;100 .mu.m and a binder. These components are mixed and pressed, but the mixture must be heated, prior to being pressed, to a temperature at which the binder becomes liquid. A disadvantage of this known method is that the finest component, which has a grain size of less than 100 .mu.m and is very difficult to process, is limited to a maximum of 25% of the briquette mixture. The reason that this is unfortunate is that dust in this grain size spectrum constitutes by far the largest part of the waste products accumulated. In addition, a continuously operating platform conveyor oven is required to heat the mixture so as to liquify the binder. According to the method described in DE-AS No. 23 61 742, sludge is an absolutely essential component of the mixture, and thus it is not immediately clear how the residual matter, which accumulates only in the dry state can be processed for recovery.
The same thing applies to the method described in DE-AS No. 25 31 457, in which the sludge component must first be dehydrated down to a water content of 2 to 15% by weight before the binder and the dust component are admixed. This latter method requires heating the briquettes to 350.degree. C. to remove the residual moisture and is, therefore, relatively elaborate and expensive.
According to DE-AS No. 24 27 619, finely divided wastes that contain carbon and at least 5% iron are mixed with a bituminous binder, the mixture is formed into briquettes, and the briquettes are treated for 30 to 90 minutes with an oxygen-containing gas at 170.degree. to 320.degree. C. This heat treatment, however, is expensive and is to be applied only: (a) to the wastes accumulating in the production of iron and steel in powder or dust form, i.e., blast-furnace flue dust, converter dust, rolling scale, coke dust and flux; or (b) to the scrap from foundries and machine shops, namely, lathe and drill press chips. Mixtures of fine with coarse grain fractions are not treated by this method. If chips are used, their dimensions should not exceed 6 mm; if necessary, they are to be comminuted, which increases the cost.